ENABLE_THUMBNAIL_GENERATOR -> WIP: Refactoring and preparation for adding thumbnails to exported gcode and 3mf files

src/libslic3r/GCode/ThumbnailData.hpp

@@ -16,6 +16,8 @@ struct ThumbnailData
     ThumbnailData() { reset(); }
     void set(unsigned int w, unsigned int h);
     void reset();
+
+    bool is_valid() const;
 };
 
 } // namespace Slic3r